1. Field of the Invention
The present invention relate to an exposure apparatus and an exposure method used in a photolithography process for producing a semiconductor device, a liquid crystal display, an image pickup device, a thin film magnetic head and other micro device and a method of producing devices using the method.
2. Description of the Related Art
When producing a micro device, such as a semiconductor device, liquid crystal display, image pickup device (CCD, etc.), thin film magnetic head, etc. by using a photolithography technique, an exposure apparatus for performing projection exposure of an image of a reticle pattern as a mask on a wafer (or a glass plate, etc.) being coated a photo resist, etc. via a projection optical system is used.
In such an exposure apparatus, a wavelength of an exposure light has ben made shorter to improve resolution of a pattern to be formed on a wafer along with micro devices becoming minute. Due to this, the exposure light to be used has shifted from a g-ray (a wavelength of 436 nm) and an i-ray (a wavelength of 365 nm) by a high-pressure mercury lamp to a KrF excimer laser (a wavelength of 248 nm) and an ArF excimer laser (a wavelength of 193 nm). Also, to deal with further higher resolution, use of an F2 laser (a wavelength of 157 nm) has been recently studied.
A light oscillated from the F2 laser is so-called a vacuum ultraviolet ray, which is almost incapable of transmitting in the air because it is absorbed by substances, such as oxygen, water or organic materials. Thus, when it is used as an exposure light, it is necessary that a light path thereof is made vacuum or filled with an inert gas, such as helium (He), neon (Ne), argon (Ar), krypton (Kr), and other inert gases and nitrogen (N2), which allows a light having a wavelength of about 157 nm pass through it.
Also, in the above exposure apparatus, a variety of light sensors (photodetectors) are permanently provided for monitoring whether exposure amount control for keeping an exposure amount (cumulative exposure energy) in a suitable range for every spot in respective shot regions of a wafer and an exposure light (exposure region) keeps a suitable condition without illuminance unevenness, and monitoring whether the light path in kept under a suitable environment for the exposure light to transmit, etc. and energy (illuminance, an amount of light, intensity, etc.) of the exposure light is measured. As a light sensor for such measurement, a silicon photodiode, pyroelectric or thermal actinometer is often used in terms of performance and costs.
Here, when adopting the above F2 laser as a light source, the F2 laser exhibits a characteristic of oscillating a vacuum ultraviolet ray (hereinafter, also referred to as a main light) having a wavelength of 157 nm and collaterally generating a red light (hereinafter, also referred to as a sub light) having a wavelength of 630 to 720 nm or so, which does not contributes to exposure. Intensity of the sub light is about 5 to 10% of the total immediately after emitted from the F2 laser. The sub light exhibits almost no attenuation due to an optional system composing the light path of the exposure light, so it reaches to a light sensor along with the main light.
While, a silicon photodiode and a pyroelectric or thermal actinometer as above used as a light sensor are sensitive not only to the wavelength of the main light but to that of the sub light, so they also detect the sub light and cannot accurately measure a light amount of the main light which contributes to exposure. Thus, there in a disadvantage that exposure amount control is not suitably performed and a highly fine pattern cannot be formed in some cases.
Further, when monitoring entering of the air to the light path and generation of impurities by using a result detected by a light sensor, since attenuation of the main light in much while that of the sub light is little and detected by the light sensor, processing may be continued by judging that there is no problem even in the case here actually the operation has to be halted due to an error, which in a crucial matter.
An object of the present invention is to enable accurate measurement of energy of a main light, exposure amount control and other failure monitoring, etc. at high accuracy even in the case of using a light source which also generates collaterally an unnecessary sub light long with an oscillation of a main light having a wavelength to expose a substrate.
According to a first aspect of the present invention, there is provided an exposure apparatus which exposes a substrate via a mask being formed a pattern, comprising a light source which emits a light including a main light having a wavelength to expose the substrate and a sub light having a different wavelength from that of the main light collaterally generated in accordance with an oscillation of the main light; a main optical system which introduces a light from the light source to the substrate via the mask; a light sensor having sensitivity to a wavelength including at least the main light; and a separation device disposed on a light path from the light source to the light sensor, which separates the main light and the sub light.
According to the present invention, as a result that the separation device which separates the main light and the sub light is disposed on th light path from the light source to the light sensor, only the main light can incident on the light sensor and a detection error caused by also detecting the sub light can be reduced.
When the above exposure apparatus is provided with a branch optical system which introduces a part of the light from the main optical system to the light sensor, the separation device can be provided between the branch optical system and the light sensor. Due to the provision of the separation device inside the branch optical system which introduces the light to the light sensor, attenuation of the light passing the main optical system caused by the separation device can be eliminated.
The exposure apparatus may be further comprised with a control device which controls a cumulative light amount on the substrate based on the main light separated by the separation device. The control device is capable of controlling the cumulative light amount based on a measurement result only of the main light by the light sensor, so an effect of the sub light can be excluded and accurate control can be performed.
In the exposure apparatus, a shift device which selectively shifts the separation device between a first position of being out of a light path of the light branched by the branch optical system and a second position placed on the light path can be provided. In this case, a correction device which corrects a measurement result by the light sensor when the separation device is shifted to the first position based on a measurement result by the light sensor when the separation device is shifted to the second position can be further provided.
When measuring by the light sensor by setting the separation device at the first position (position out of the light path), a light not separated to the main light and the sub light irradiates on the light sensor. On the other hand, when measuring by the light sensor by setting the separation device at the second position (position on the light path), only the sub light can irradiate on the light sensor. As a result, an accurate measurement result of the main light excluding the sub light can be obtained from measurement results of both.
As the separation device, an optical filter which transmits a light of a wavelength range including a wavelength of the main light and attenuates a light of a wavelength range including a wavelength of the sub light, or a reflective transmissive type mirror (dichroic mirror) which reflects the light of the wavelength range including the wavelength of the main light and allows the light of the wavelength range including the wavelength of the sub light pass through it can be adopted. Here, the word xe2x80x9cattenuatesxe2x80x9d includes a completely light-blocking case and a case of not completely blocking but transmitting a part thereof (for example, a came where the transmission amount is not more than minimum detection sensitivity of the light sensor).
The present invention is particularly preferable when using an F2 laser light source as the above light source. Namely, the F2 laser light source oscillates an a main light a light of 157 nm while also generates a red light (a wavelength of 630 to 720 nm or so) as a sub light, but it is possible to accurately measure only the main light excluding the red light in this case. As a result, control of a cumulative exposure light amount can be suitably performed and accuracy of a variety of failure monitoring can be improved.
According to a second aspect of the present invention, there in provided an exposure apparatus which exposes a substrate via a mask being formed a pattern, comprising a light source which emits a light including a main light having a wavelength to expose the substrate and a sub light having a different wavelength from that of the main light collaterally generated in accordance with an oscillation of the main light; a main optical system which introduces a light from the light source to the substrate via the mask; a first light sensor having sensitivity to a wavelength range including wavelengths of the main light and the sub light; a second light sensor having sensitivity to a wavelength range including at least a wavelength of the sub light; a first branch optical system disposed on a light path from the light in the main optical system, which introduces a part of the light to the first light sensor; a second optical system disposed on a light path of the light in the main optical system or in the first branch optical system, which introduces a part of the light to the second light sensor; and a separation device disposed between the second branch optical system and the second light sensor, which separates the main light and the sub light. In this case, a correction device which corrects a result measured by the first light sensor based on a result measured by the second light sensor can be further provided. The second light sensor nay be sensitive to the main light.
The light not separated to the main light and the sub light irradiates on the first light sensor. On the other hand, only the sub light can irradiate on the second light sensor. Accordingly, by correcting a measurement result by the first light sensor based on the measurement result by the second light sensor, an accurate measurement result of the main light excluding the sub light can be obtained.
According to a third aspect of the present invention, there in provided an exposure method for exposing a substrate by using an exposure light including a main light having a wavelength to expose the substrate and a sub light having a different wavelength from that of the main light via a mask being formed a pattern, including the steps of separating the sub light from the exposure light including the main light and the sub light; measuring energy (a light amount, intensity, illuminance, etc.) of the exposure light after the separation; and controlling a cumulative exposure light amount on the substrate based on the measurement result.
According to a fourth aspect of the present invention, there is provided an exposure method for exposing a substrate by using an exposure light including a main light having a wavelength to expose the substrate and a sub light having a different wavelength from that of the main light via a mask being formed a pattern, including the steps of branching a part of the exposure light including the main light and the sub light; separating the sub light from the branched exposure light; measuring energy of the exposure light after the separation; and controlling a cumulative exposure light amount on the substrate based on the measurement result.
According to a fifth aspect of the present invention, there is provided an exposure method for exposing a substrate using an exposure light including a main light having a wavelength to expose the substrate and a sub light having a different wavelength from that of the main light via a mask being formed a pattern, including the steps of measuring first energy of the exposure light including the main light and the sub light; separating the main light from the exposure light including the main light and the sub light; measuring second energy of the exposure light after separating the main light; and correcting the first energy based on the second energy and controlling a cumulative exposure light amount on the substrate based on the corrected first energy.
According to the exposure method according to the above third to fifth aspects of the present invention, the main light excluding the sub light can be measured accurately. These methods are particularly preferable when the light including the main light and the sub light is a laser emitted from the F2 laser light source.
According to a sixth aspect of the present invention, there is provided a method of producing a device including a step of transferring an image of the mask pattern to the substrate by using the exposure method according to the above third to fifth aspect of the present invention.